Navigate

A lens having focal length f and aperture of diameter d forms an image of intensity I

A lens having focal length f and aperture of diameter d forms an image of intensity I. Aperature of diameter d/2 in central region of lens is covered by a black paper. Focal length of lens and intensity of image now will be respectively:

Options

(a) f and I/4
(b) 3f/4 and I/2
(c) f and 3I/4
(d) f/2 and I/2

Correct Answer:

f and 3I/4

Explanation:

By covering aperture, focal length does not change. But intensity is reduced by 1/4 times, as aperture diameter d/2 is covered.
I’ = I – I / 4 = 3I / 4
New focal length = f and intensity = 3I / 4

AIPMT2010
admin:

Related Questions

  1. Application of a forward bias to a P-N junction
  2. A circular disc rolls down an inclined plane.The ratio of rotational kinetic energy
  3. When the wavelength of sound changes from 1 m to 1.01 m,
  4. A double slit experiment is performed with light of wavelength 500 nm. A thin film
  5. Two bodies of masses m₁ and m₂ and having velocities v₁ and v₂ respectively